Systematic Investigation into Biochar-Mediated Suppression of Asphalt Rubber Fumes: Inhibition Mechanism, Pollutant Profiles, and Binder Performance

Asphalt rubber (AR) is increasingly used as a sustainable pavement binder, but hazardous fumes generated during production constrain its wider application. This study investigated wood biochar (WB), walnut-shell biochar (WSB) and corn-straw biochar (CSB) as sustainable fume-suppressing additives for AR binders. The biochars were characterized by scanning electron microscopy (SEM), elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and N2 physisorption tests, while AR emissions were evaluated through real-time monitoring of total volatile organic compounds (TVOC), H2S, SO2 and NOX, together with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) analysis. Conventional binder properties and rheological behavior were also evaluated. The results showed that WSB possessed the most developed hierarchical pore structure, with a Brunauer–Emmett–Teller (BET) surface area of 285.8 m2/g and a total pore volume of 0.165 cm3/g, achieving the strongest TVOC reduction (65.6%) and the lowest detectable organic-fume complexity. TD-GC-MS analysis showed that WSB mainly reduced the relative responses of aliphatic hydrocarbons and PAH-related hydrocarbons, whereas WB selectively reduced BTEX/alkylbenzenes and S/N-containing responses. CSB, enriched in ash-derived minerals and oxygen-containing groups, exhibited the strongest sulfur-gas suppression, achieving complete SO2 elimination and 57.65% H2S inhibition, but also induced a redistribution toward oxygenated organics and alicyclic hydrocarbons. Biochar addition generally improved high-temperature stiffness and compatibility. These findings demonstrate feedstock-dependent and pollutant-specific suppression behavior, suggesting that physical adsorption and surface chemical interactions may jointly contribute to fume suppression, and provide guidance for selecting biochar additives for cleaner AR production.